CLEVELAND, Ohio - More than 12,000 structures - houses, schools, former manufacturing plants and forgotten warehouses - sit empty in the city of Cleveland. Roughly half of them are so dilapidated that they're possibly beyond saving.

These buildings taint neighborhoods, hurt home values and entice criminals. Shabby houses stand as testaments to a half-century of population loss capped by a decade-long flood of foreclosures and a brutal housing bust.

An unprecedented, citywide survey of 158,851 properties completed last month shows the scope of the problem, particularly on the hard-hit East Side.

Surveyors dispatched by the Thriving Communities Institute, an urban-focused arm of the nonprofit Western Reserve Land Conservancy, found that 8.8 percent of residential structures in the city are vacant. More than a third of those empty homes might be a lost cause.

Rust Belt cities with too many houses for too few residents are trying to quantify and track blight, in an attempt to shape public policy and support their bids to secure scarce federal and state demolition funds. Cleveland's building department periodically sends out investigators to count vacant homes. But the city uses paper forms, not digital databases. And the city reports aren't comprehensive.

The Thriving Communities survey relied heavily on private funding, with a $20,000 assist from Cleveland City Council. With better technology and a 16-person survey team, the nonprofit dug deeper than the city has, or can.

The resulting data (presented, in part, in the interactive map that accompanies this story) spans all sorts of properties, from tiny bungalows to shopping centers to vacant lots. The database assigns a letter grade of A through F to every building. And surveyors took note of everything from the condition of windows and paint to the presence of sidewalks, trees and trash.

The upshot: Cleveland's likely demolition pipeline comes to just over 6,100 buildings, roughly 5 percent of all the structures that surveyors visited.

It would cost well over $60 million to knock them down.

Here's the good news: The blight isn't as bad as it appeared, based on past estimates from the city and other researchers.

"It's not all doom and gloom," said Jim Rokakis, director of Thriving Communities and a former Cuyahoga County treasurer. "You've got neighborhoods that are in great condition. There are people who have a lot of faith in their neighborhood. They're keeping their houses in good shape. They have some pride."

The pool of deeply tainted properties actually has been shrinking, thanks to demolition, fewer foreclosures and a healthier housing market. The tally of decrepit houses fell from 2013, when the city found more than 7,700 distressed or empty homes. Nearly every neighborhood saw improvement.

But it's clear that large sections of the city still are far from feeling the renaissance that is luring investors to downtown and a few rebounding districts.

"We are every bit as focused on dealing with this issue as we were in the midst of the recession," Ken Silliman, chief of staff to Mayor Frank Jackson, said of vacancy and abandonment.

"Even though we may be turning a corner in terms of the volume of vacant and distressed properties, 6,000 is way more than we want to see in the city of Cleveland," he added. "And if you happen to be a resident who is right next to one or more vacant or distressed structures, you don't care about whether the long-term trends are favorable. What you care about is getting that blighted structure out of your neighborhood."

The sad state of some properties in the city isn't just a problem for next-door neighbors.

Neglected houses and crumbling commercial buildings cast a regional pall. Since 2006, the combined tax value of pre-existing residential properties in Cleveland has fallen by more than 31 percent, according to data provided by Ken Surratt, deputy director of housing for Cuyahoga County. That decline is leveling off, but a weaker city shifts a greater burden onto the suburbs, to communities where values didn't fall so far or stay depressed for as long.

In some parts of Cleveland, the median sale price for a home was less than $20,000 through the first seven months of this year, based on data collected by Case Western Reserve University and analyzed by Frank Ford, a senior policy advisor at Thriving Communities. Some of the lowest sale prices pop up in neighborhoods with the highest share of vacant homes, including St. Clair-Superior, Glenville and Hough.

Vacancy isn't the sole reason for depressed home values. And razing empty buildings isn't a cure-all. But a recent study in Detroit found that each demolition in hard-hit areas of the city boosted the value of occupied houses within 500 feet by 4.3 percent. Property values rose even more in areas seeing a mix of demolitions, land-bank home auctions, side-lot sales to neighbors and tidying of vacant lots.

Rokakis believes some neighborhoods in Cleveland have little chance of recovery until the blight is cleared.

"Short-term, I don't think we can make the promise that it's going to increase your property value," he said of demolition. "But common sense tells you that if you're living in a sea of vacant properties, there's no hope in that neighborhood. None. You can't even talk about rebirth."

The Thriving Communities findings will start trickling out online this week. A detailed report is due out in the spring. During the next few months, researchers plan to add crime data, lead-poisoning statistics and other figures to their property map as they look at the links between abandoned buildings, safety and public health. (Search a property database here.)

The Cleveland Foundation contributed nearly $120,000 to the survey project. Detroit-based Rock Ventures, the umbrella company for Cleveland Cavaliers' owner Dan Gilbert's various businesses, kicked in $25,000. In that way, Cleveland is similar to other cities where private and philanthropic groups are trying to tackle housing problems that local governments can't solve by themselves.

A 2009 study of Detroit - a city with 2.5 times the number of residential parcels found in Cleveland - turned up more than 33,500 empty homes. In East Cleveland, a city that spans just 3.1 square miles, Thriving Communities found a vacancy rate of nearly 24 percent last year. A similar study of Akron identified 4,600 vacant buildings, though only 500 of those structures appeared severely distressed.

In Akron, 4.7 percent of all the properties listed in the survey were vacant. In Cleveland, that number was closer to 7.7 percent.

Ron O'Leary, the city's director of building and housing, said the data prove the worth of demolition campaigns waged since the housing market collapsed. The city expects to use the survey results to better target future spending and to shape strategies for planting trees, fixing sidewalks and policing illegal dumping on lots.

"We still have a lot of work to do to remove blighted structures from the city of Cleveland," he said. "Having these kinds of specific numbers and a survey of structures in the city helps us to explain our aggressive start in 2006, 2007 and to pursue government sources of funding.

"The last thing that we noticed in the data," he added, with some relief, "was just the number of properties that are in the A and B classification. It did indicate that there are a high percentage of structures that are occupied, that are well-maintained."

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Scroll, zoom, and click on properties in this interactive map to view some of the data collected by a survey team working for the Thriving Communities Institute program of the Western Reserve Land Conservancy.

Explanation of the letter grades:

A: Excellent. The structure is new, newly renovated or well maintained and cared for. No visible deterioration, historic detailing, unique.